Transcript Document

Species Interactions
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Competition: (-,-) interaction
Mutualism: (+, +) interaction
Commensalism: (+, 0) interaction
Exploitation: (+, -) interaction
Competition
• Def’n: Mutually adverse interaction between
organisms that use a shared resource that is in
limiting supply
• Interaction: ( -,- )
Effect on Sp. 1
Effect on Sp. 2
Plant Competition
• Light very important: explains trees!
Competition: (-,-) interaction
• Interference Competition:
– Individuals interact directly to limit one
another’s access to resource
• Resource Competition:
– Individuals interact with resource in effort to
obtain more. Once gained, resource unavailable
to competitor.
Resource competition
• Example: creosote bush (Larrea tridentata)
• Important desert shrub
Resource competition
• Avoidance of root overlap
Interference Competition:
Allelopathy
• Allelopathy: chemical released by one plant species
negatively impacts another
• Differs from resource competition, where resources
removed from environment
• In allelopathy chemicals are added to environment
Examples
• Some of these chemicals inhibit other plants
• Example, Salvia (sage) in coastal sage scrub (California)
Examples
• Releases cineole and
camphor from leaves
• Inhibit germination &
growth of annual plants
• In grassland, “bare zones”
around shrub borders
camphor
Weeds and allelopathy
• Example, Centaurea maculosa
(spotted knapweed)
• Major invasive nonnative weed
Weed example
• Example, Centaurea maculosa (spotted
knapweed)
• Releases catechin into soil
• When absorbed by roots of other plant species,
causes wave of cell death to move up roots into
stems
• Aids invasiveness
catechin
Pattern
• Pattern: placement of individuals of a
species relative to each other or members of
another species
• Important for sessile organisms (ex, plants)
• May reveal species interactions
– Positive may result in clumping
– Negative may result in wide spacing
Pattern
• Patterns:
– Clumped distribution (positive interaction)
– Distances less than expected compared to
random
Pattern
• Patterns:
– Uniform distribution (negative interaction)
– Distances greater than expected compared to
random
Pattern
• Patterns:
– Random (no association)
– Individuals dispersed without influence by
another’s location
Prediction?
• What pattern predicted for creosote bushes?
• Clumped, uniform, random?
Species Interactions
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Competition: (-,-) interaction
Mutualism: (+, +) interaction
Commensalism: (+, 0) interaction
Exploitation: (+, -) interaction
Mutualism: (+, +) interaction
• Example:
• Lichens: partnership between fungi and
unicellular photosynthesizer (green alga or
cyanobacteria)
Lichen
• Fungus forms body, obtains
photosynthate from partner
• Together, can colonize harsh
environments.
Mycorrhizae
• Mycorrhizae: Association of fungus with plant root
• Common: 90% of plants do this!
• Exceptions:
– Aquatic vascular plants
– Cabbage family
Mycorrhizae
• Fungus extends into soil (up to 8m away!) and aids
in uptake of nutrients (P, Zn, Cu in particular) and
possibly water for plant
• Fungus obtains sugars from plant
Mycorrhizae
• Important in revegetation/reclamation of disturbed
areas: if fungi not present, plants don’t do well!.
Revegetating a mine
Plant on left grown
without mycorrhizal fungi
Nitrogen Fixation
• Nitrogen: lots in atmosphere (79% N2)
• But plants can’t use that
• Nitrogen fixation: bacteria use N2 to form
NH3 (ammonia) or NO3- (nitrate)
Nitrogen Fixation
• Special ways to get N:
– Symbiotic bacteria: many legume plants form
nodules on roots.
– Rhizobium (N-fixing bacterium) inhabit, obtain
sugars, provide plant with N
Defensive mutualisms
• Typically between plants and insects
• Insect gets home/food, plant gets protection from
herbivory/competitors/hazards
Defensive mutualisms
• Example, Acacia and acacia ants
• Acacia, trees/shrubs in legume family. Some of those in
Central America have large hollow stipular spines
• Ants nest in spines
Defensive mutualisms
• Example, Acacia and acacia ants
• Leaves have extrafloral nectary at base (makes nectar but
not produced on a flower)
• Young leaflets have Beltian Bodies (protein rich) at tips
Defensive mutualisms
• Benefits to plant:
• Ants eat insect herbivores
• Ants are territorial and defensive and
attack herbivores not useful for food
(even humans)
• Ants clear area below shrub: removes
competitors, protects shrub (and ants!)
from fire
Species Interactions
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•
Competition: (-,-) interaction
Mutualism: (+, +) interaction
Commensalism: (+, 0) interaction
Exploitation: (+, -) interaction
Commensalism: (+, 0) interaction
• Interaction that benefits one species but has no effect
on other
• Plant/plant examples:
– some epiphytes
– “nurse plant effect”
Example: some epiphytes
• Epiphyte: Plant that grows on surface of other plants
• Example:
– Spanish moss
Example: some epiphytes
• Epiphyte: Plant that grows on surface of other plants
• Example:
– Lots in wet tropics
Commensalism
• Nurse plant effect (+, 0)
• Larger plant provides favorable microhabitat for
seedlings of another species (+)
• Seedling so small it has no effect on larger plant (0)
Commensalism
• Example,
• Saguaro cactus (Carnegiea
gigantea)
• Large individuals hundreds of
years old
Commensalism
• Seedlings found only under
shrubs/trees
• Particularly Palo Verde trees
Species Interactions
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Competition: (-,-) interaction
Mutualism: (+, +) interaction
Commensalism: (+, 0) interaction
Exploitation: (+, -) interaction